Then perhaps the OP is right in that his plan is the best of bad options? (the worse options being, to break the promise to son and let him be bored, or to take him back early, etc.)

Plan A had been to find same age neighbours. OP is now at Plan B...

One obvious thing to check: the boy is at an international school in the morning. Has he found any friends at the said international school, who could hang out with him after school?

In any case, hiring the 23 year old girl with nephews included sounds even better than plan A. Whether hanging out with same age neighbours from the house or same age international school friends, this would have meant foreign child/ren without any adult guide/chaperone responsible to care for them. So getting him into a family with a young aunt hired to help/huide the bunch would seem safer.